Agar (or libAgar)
is a cross-platformGUI toolkit.
Agar provides a base framework and a set of widgets from which graphical
applications can be built which run natively under
X11,
Windows,
MacOS X,
SDL
and others.
Agar takes advantage of texture memory and hardware acceleration wherever
available.
Agar may also attach to an existing SDL or
OpenGL context and operate as
a self-contained windowing GUI for the application.
Agar can be compiled with zero dependencies (although
FreeType
is recommended).
The API is thread-safe unless documented otherwise.

Agar is free software. Its source code is freely usable and re-usable by
everyone under a BSD license, which allows
use in commercial applications free of charge.
The best available version is
1.5.0.